PL212104B1 - Multilayer magnetic reflecting pigment flakes and foils - Google Patents

Abstract

Multilayered magnetic pigment flakes and foils are provided. The pigment flakes can have a stacked layer structure on opposing sides of a magnetic core, or can be formed as an encapsulant structure with encapsulating layers around the magnetic core. The magnetic core in the stacked layer structure includes a magnetic layer that is sandwiched between opposing insulator layers, which in turn are sandwiched between opposing reflector layers. Similarly, the magnetic core in the encapsulant structure includes a magnetic layer that is surrounded by an insulator layer, which in turn is surrounded by a reflector layer. The insulator layers in the pigment flakes substantially prevent corrosion of the flakes when exposed to harsh environments. Some embodiments of the pigment flakes and foils exhibit a discrete color shift at differing angles of incident light or viewing. The pigment flakes can be interspersed into liquid media such as paints or inks to produce colorant compositions for subsequent application to objects or papers. The foils can be laminated to various objects or can be formed on a carrier substrate.

Description

The invention relates to pigment flakes having a central magnetic layer and two reflector layers, which flakes exhibit variable optical characteristics.

Various pigments, dyes and films are known for a wide range of applications. For example, magnetic pigments are used to decorate kitchen utensils, create surfaces with different patterns, and prepare protective materials. Color change pigments are used in cosmetics, inks, opaque materials, decorations, ceramics, car paints, anti-counterfeit holograms and anti-counterfeit inks used to secure documents and money.

The color shifting pigments, dyes and films exhibit the property of changing color when influenced by changing the angle of incidence of light or by changing the viewing angle of the observer. The color change by pigments and films can be controlled by the appropriate design of thin optical films or the orientation of the molecular molecules that make up the structure that covers the flake or film. The desired effects can be achieved by changing parameters such as the thickness of the layers forming the flakes and films and the refractive index of each layer. Variation in perceived color for different viewing angles or incidence angles is the result of a combination of selective absorption by materials having layers and wavelength dependent interference effects. The interference effects resulting from the superposition of light waves that are reflected multiple times are responsible for changes in the color perceived from different angles. The maximum reflectance values change in position and intensity as the viewing angle changes due to changes in interference effects due to differences in the path length of the light in different layers of the material, which are selectively amplified at particular wavelengths.

Various methods have been used to achieve such color shifting effects. For example, small multilayer flakes, usually consisting of multiple layers of thin films, are dispersed in a medium such as paint or ink, which can then be applied to the surface of the object. Optionally, such flakes may be coated to achieve desired colors and optical effects. Another approach is to encapsulate small metallic or silicon supports in different layers and then disperse the encapsulated supports in a medium such as paint or ink. Furthermore, films are known which consist of multiple layers of thin films on a carrier material.

One way to produce a multilayer thin film structure is to form a layer on a pliable fabric material with subsequent release. The various layers are applied to the fabric by methods well known in the art for forming thin film structures such as PVD, sputtering, or the like. The multilayer thin film structure is then removed from the fabric material as thin film color shifting flakes that can be added to a polymeric medium such as various pigment media for use as ink or ink. In addition, ink or ink additives may be added to the color shifting flakes to obtain the desired color shifting effects.

Color shifting pigments or films can be made from a multilayer thin film structure which includes the same base layers. They contain an absorber layer (s), a dielectric layer (s) and optionally a reflector layer in a different order of stacking of the layers. The coatings are manufactured to have a symmetrical multilayer thin-cell structure such as:

absorber / dielectric / reflector / dielectric / absorber; or absorber / dielectric / absorber.

The coatings can also be made to have an asymmetric multilayer thin film structure such as an absorber / dielectric / reflector.

With respect to magnetic pigments, US Patent No. 4,838,648 to Phillips et al. (Hereinafter "Phillips' 648") discloses a magnetic color shifting thin film structure in which a magnetic material can be used as a reflector or absorber layer. One of the disclosed magnetic materials is a cobalt-nickel alloy. Phillips' 648 discloses flakes and films with the following structures: dye top layer / absorber / dielectric / magnetic layer / substrate; dye top layer / absorber / dielectric / magnetic layer / dielectric / absorber / dye top layer; and

Binder / magnetic layer / dielectric / absorber / releasable hard coat / substrate.

WO 03000801 discloses multilayer pigment flakes in which the magnetic layer is covered with a dielectric layer; the magnetic layer serves as a reflector layer and the petals according to this embodiment do not have an additional reflector layer.

One attempt to incorporate a magnetic layer into a multilayer flake is disclosed in EP 686675B1 to Schmid et al. (Hereinafter "Schmid"), which describes color shifting laminar structures comprising a magnetic layer between a dielectric layer and an aluminum center layer as shown. :

oxide / absorber / dielectric / magnet / Al / magnet / dielectric / absorber / oxide

In this way, Schmid uses aluminum plates and then covers these plates with magnetic materials. The superimposed magnetic material reduces the reflective properties of the pigment (aluminum is the second shinest metal after silver) and thus any magnetic material is less reflective.

Accordingly, there is a need to improve magnetic pigment flakes and films that overcome or avoid the imperfections of previous flakes and films.

The present invention relates to multi-layer pigmented flakes having magnetic properties.

The invention relates to a magnetic pigment flake comprising: a central magnetic layer having a first major surface, an opposing second major surface and at least one side surface, a first reflector layer, and a second reflector layer each comprising one or more metals or metal alloys, characterized by: that it additionally comprises a first insulator layer positioned on the first major surface of the magnetic layer and a first reflector layer positioned on the first insulator layer, a second insulator layer positioned on the second major surface of the magnetic layer and a second reflector layer positioned on the second major surface of the insulator, wherein comprises an electrically insulating material and is at least 10 nm thick, the magnetic layer is 20 to 3000 nm thick and the reflector layer is 20 to 1000 nm thick; and the pigment flake exhibits a reflectance corresponding to that of the first and second reflector layers, and exhibits magnetic properties depending on the magnetic layer.

The first and second insulator layers in the magnetic pigment flake according to the invention preferably contact and cover the side surfaces of the middle magnetic layer, surrounding the central magnetic layer, and that the first and second reflector layers contact and surround the insulator layer that surrounds the middle magnetic layer.

In the magnetic pigment flake according to the invention, preferably the first and second insulator layers are provided exclusively on the first major surface of the magnetic layer and the second major surface of the magnetic layer, or preferably the first and second insulator layers are on the first major surface of the magnetic layer and the second major surface of the magnetic layer, and on one side surface of the magnetic layer.

According to the invention, preferably the first and second reflector layers form part of an adjacent reflection layer surrounding the magnetic layer and the insulator layer.

The magnetic pigment flake of the invention is preferably characterized in that the magnetic layer comprises a material having a coercivity of less than about 159.155 A / m (2000 Oe), more preferably less than about 23.873 A / m (300 Oe).

The magnetic layer preferably comprises a material selected from the group consisting of iron, nickel, cobalt, gadolinium, terbium, dysprosium, erbium and their alloys or oxides.

The magnetic layer preferably comprises a material selected from the group consisting of Fe / Si, Fe / Ni, Fe / Co, Fe / Ni / Mo, and combinations thereof.

The magnetic layer comprises a material preferably selected from the group consisting of SmCo5, NdCo5, Sm2Co17, Nd2Fe14B, TbFe2 and combinations thereof.

The magnetic layer comprises a material preferably selected from the group consisting of Fe3O4, NiFe2O4, MnFe2O4, CoFe2O4, YIG, GdIG and combinations thereof.

The insulator layers preferably include a dielectric material.

The insulator layers preferably include at least one material selected from the group consisting of alumina, magnesium fluoride, nickel oxide, and combinations thereof.

PL 212 104 B1

The reflector layers include a reflective material selected from the group consisting of aluminum, silver, copper, gold, platinum, tin, titanium, palladium, nickel, cobalt, rhodium, niobium, chromium, iridium, and combinations or alloys thereof.

The invention also relates to a magnetic pigment flake comprising: a central magnetic layer having a first major surface, an opposite second major surface, and at least one side surface; a first reflector layer and a second reflector layer; each comprising one or more metals or metal alloys, further comprising a first insulator layer disposed on the first major surface of the magnetic layer and a first reflector layer disposed on the first insulator layer, a second insulator layer disposed on the second major surface of the magnetic layer, and a second reflector layer disposed on the second insulator layer, wherein the first and second insulator layers comprise an electrically insulating material and have a thickness of at least 10 nm; the thickness of the magnetic layer is from 20 to 3000 nm and the thickness of the reflector layer is from 20 to 1000 nm;

and comprises a first dielectric layer on the first reflector layer, a second dielectric layer on the second reflector layer, a first absorber layer on the first dielectric layer, a second absorber layer on the second dielectric layer; and the pigment flake has a reflectance corresponding to the reflectance of the first and second reflector layers, and exhibits magnetic properties depending on the magnetic layer, the pigment flake having a distinct color change in that the pigment flake has a first color at a first angle of incidence of light or viewing; and a second color, different from the first color, at a second light incidence or viewing angle.

The first and second dielectric layers of the magnetic flake preferably comprise a dielectric material having a refractive index of 1.65 or less.

The first and second dielectric layers preferably include a dielectric material having a refractive index greater than 1.65.

The first and second reflector layers preferably form part of an adjacent reflection layer surrounding the magnetic layer and the insulator layer, the first and second dielectric layers form part of the contiguous dielectric layer surrounding the adjacent reflector layer, and the first and second absorber layers form part of the contiguous layer surrounding the adjacent dielectric layer. .

The magnetic pigment flake preferably comprises a first transparent coating applied to the first absorber layer and a second transparent coating applied to the second absorber layer.

The invention also relates to a magnetic pigment flake comprising:

a central magnetic layer comprising a metal or metal alloy and a reflector layer comprising one or more metals or metal alloys and surrounding the central magnetic layer, characterized in that it comprises an insulator layer sandwiched between the central magnetic layer and the reflector layer surrounding the magnetic layer, wherein the insulating layer comprises an electrically insulating material and has a thickness of at least 10 nm; the thickness of the magnetic layer is from 20 to 3000 nm and the thickness of the reflector layer is from 20 to 1000 nm; and the pigment flake exhibits a reflectance corresponding to that of the reflector layer and exhibits magnetic properties depending on the magnetic layer.

The insulator layers are preferably from about 20 nm to about 40 nm thick.

Some variants of the magnetic pigment flakes show a color change at different angles of incidence of light or viewing. The color shifting variants exhibit a marked color shift such that they have a first color at a first incidence of light or viewing angle and a second color different from the first color at a second light incidence or viewing angle.

Pigment flakes can be dispersed in liquid media such as paints or inks to form dye compositions which are then used to coat objects or paper. The films can be laminated to a variety of items or they can be formed on a carrier substrate.

Description of the drawings

In order to illustrate the above and other features of the present invention, a more detailed description of the invention will be made by reference to specific embodiments thereof which are set forth in the accompanying drawings. It is understood that these drawings show only the typical ones

Variations of the invention are therefore not considered as limiting the scope thereof. The invention will be described and explained in additional detail and detail through the use of the accompanying drawings in which:

Fig. 1 is a schematic representation of a coating structure of a magnetic pigment flake according to one embodiment of the invention;

Fig. 2 is a schematic representation of a coating structure of a magnetic pigment flake according to a further embodiment of the invention;

Fig. 3 is a schematic representation of a coating structure of a magnetic pigment flake according to a further embodiment of the invention;

Fig. 4 is a schematic representation of a coating structure of a magnetic pigment flake according to alternative embodiments of the invention; and

Fig. 5 is a schematic representation of the shell structure of the magnetic foil.

The present invention relates to multi-layer pigment flakes that can be used to produce security features that are not visually discernible, to create illusory or three-dimensional images for security devices, or to impart decorative features to a product. Unlike many conventional magnetic flakes, the flakes of the invention not only consist of magnetizable materials but contain both magnetizable and non-magnetizable materials. The invention includes pigmented flakes in which an insulator layer is sandwiched between the magnetic layer and the reflector layer. The insulator layer in pigmented flakes and films essentially prevents corrosion of the flakes when exposed to harsh environmental conditions.

It has been found that a magnetic pigment having a magnetic layer adhering to a metal reflector layer such as aluminum is better suited to a temperature and humidity controlled environment. Under severe environmental conditions such as open air, high humidity, salt spray or solution, such a magnetic pigment degrades due to galvanic corrosion of a more electronegative metal such as aluminum.

Galvanic corrosion (also called dissimilar metal corrosion) is the process by which a material oxidizes or corrodes when it is in contact with another material under certain conditions. For galvanic corrosion to take place, three particular conditions must exist. First, two electrochemically different metals must be present. Second, the two metals must be in contact so that an electrical conduction path is created between the metals. Third, there must also be a conductivity pathway that allows the metal ions to move from a more electronegative metal (anode) to a more electropositive metal (cathode). If any of these three conditions are not present, galvanic corrosion will not occur.

In order to reduce corrosion in magnetic pigments having different metals adjacent to each other, it is sufficient to eliminate one of the three galvanic corrosion conditions described above. The easiest condition to eliminate is the electrical contact between dissimilar metals, by placing very thin insulating layers between dissimilar metals. Various variants of the pigment with such insulating layers are described in more detail below.

In various embodiments according to the present invention, the pigment flakes have significant changes in color saturation and hue with changes in the angle of incidence of light or the viewing angle of an observer. Such an optical effect known as goniochromatic or "hue shifting" allows the perceived color to change with the angle of lighting or viewing. Accordingly, such pigment flakes have a first color at a first light or viewing angle and a second color different from the first color at a second light or viewing angle. Pigment flakes can be dispersed in liquid media such as paints or inks to form various color-shifting dye compositions for subsequent coating of articles or paper.

In general, the color shifting pigment flakes according to the invention may have a symmetrical shell pile structure on opposite sides of the magnetic core layer, they may have an asymmetric shell structure with most of the layers on one side of the magnetic layer, or they may be formed from one or more closed shells which surround the magnetic core. The coating structure of the color shifting flakes includes a magnetic core which includes a magnetic or magnetizable layer and other optional layers, an insulating layer on the magnetic core, a reflector layer on an insulating layer, a dielectric layer on a reflector layer

And an absorber layer on the dielectric layer. The term "na" as used herein in reference to the relationship between layers is intended to include both adjacent and non-contiguous layers.

The present invention presents a significant improvement to the conventional magnetic pigments by achieving much higher color saturation and brightness. By placing a duller magnetic material inside the reflector, the present invention achieves two objectives: 1) the reflectance of the reflector layer is maintained, and 2) color shifting pigments without an inner core of magnetic material cannot be distinguished by an observer from such a pigment with a core of magnetic material. For example, two coated objects viewed side by side, one with and the other without magnetic material in the coating, would look the same to the observer. The magnetic color-changing pigment solves the problem of masking the security agents, regardless of the color-changing effect. For example, with a magnetic detection system, the magnetic signature hidden in the pigment could be read with a Faraday effect detector.

Illusive or 3D-like effects may be produced by exposing the pigment flakes of the invention to an external magnetic force, thereby orienting the plane of some flakes normal to the surface of the flake-containing coating. The pigment flakes not oriented by the magnetic field lie in their planar plane generally parallel to the surface of the coating. The effect of the three-dimensional image is due to the alignment of the particles so that the position ratio is oriented with the magnetic field, e.g. the longest part of the pigment flake is aligned along the magnetic field lines. Methods for producing illusory and three-dimensional images that can be applied to the magnetic pigments disclosed in this document are described in more detail in U.S. Patent Application Serial No. 09 / 850,421, filed May 7, 2001, co-pending patent pending, and entitled "Processes for Manufacturing articles covered with pictures by the use of magnetic pigments ”.

The color shifting flakes of the invention can be made using conventional thin film deposition techniques that are well known in the art for forming thin film structures. Examples (non-limiting) of such thin film deposition techniques include physical vacuum sputtering (PVD), chemical vacuum sputtering (CVD), their plasma enhanced (PE) variants such as PECVD or PECVD jet sputtering, electroplating, and other similar deposition methods that lead to the formation of clear and uniform thin film layers.

The color shifting pigment flakes according to the invention can be produced by various production methods. For example, pigment flakes may be formed by a fabric covering process in which various layers are sequentially deposited onto a fabric material using conventional deposition techniques to form a thin film structure which is then cracked and removed from the fabric such as by using a solvent in the fabric. to form multiple thin-film flakes.

In another production method, one or more thin film layers including at least a magnetic layer are deposited on a fabric to form a film, which is then cracked and removed from the fabric to form a plurality of pre-pigment flakes. The pre-flakes can be further ground by grinding if desired. The pre-flakes are coated with the next layer or layers in a sequential closed-structure formation process, resulting in multiple pigment flakes.

In another manufacturing method, the magnetic particles may be coated in a sequential closed structure building process to form a plurality of pigment flakes. When the closed structure forming process is used to form outer flake layers, it is preferred that each respective closed structure layer is a continuous layer composed of a single material surrounding the flake structure.

Referring to drawings in which similar structures are shown with like reference numerals, Fig. 1 defines a magnetic reflective petal (RMF) 20 according to one embodiment of the invention. RMF 20 may be a generally symmetrical thin film structure comprising a magnetic layer 22, a first insulator layer 25 on one major surface of the magnetic layer 22, and a second insulator layer 26 on an opposite second major surface.

The first reflector layer 27 is on the first insulator layer 25 and the second reflector layer 28 is on the second insulator layer 26.

Placing an insulator layer between the reflector layer and the magnetic layer prevents galvanic corrosion of the petal. In addition, thanks to the magnetic layer disposed between the outer reflector layers as shown in Figure 1, the optical properties of the reflector layers are not degraded and the petal remains highly reflective.

The flakes corresponding to the RMF 20 can be formed by a fabric covering process as described previously in which different layers are sequentially deposited on the fabric material to form a film structure which is then cracked and removed from the fabric to produce a plurality of flakes. Alternatively, the first and second reflector layers 27 and 28 may be formed as part of an adjacent reflector layer 29 (shown by phantom lines) substantially surrounding the magnetic layer 22 and insulator layers 25 and 26 that were previously formed by the fabric coating process.

RMF 20 can be used as a pigment flake or it can be used as a core part with additional layers thus finding use as a color changing pigment. In the case of a color shifting pigment, it is important to keep the reflectance of the reflector layer high in order to maintain the high brightness and color saturation of the pigment. Each of the layers in the RMF coating structure 20 is discussed in more detail later in this document.

Magnetic layer 22 may consist of any magnetic or magnetizable material such as nickel, cobalt, iron, gadolinium, terbium, dysprosium, erbium, and alloys or oxides thereof. For example, a cobalt-nickel alloy with a weight ratio of cobalt and nickel of about 80% and 20%, respectively, may be used. The ratio for each of these metals in the cobalt-nickel alloy can vary by plus / minus about 10% and the desired results are still achieved. Thus, cobalt may be present in the alloy in an amount from about 70% to about 90% by weight, and nickel may be present in the alloy in an amount from about 10% to about 30% by weight. Other examples of alloys include Fe / Si, Ni / Fe (e.g., permalloy), Fe / Ni, Fe / Co, Fe / Ni / Mo, and combinations thereof. Hard magnets such as SmCo5, NdCo5, Sm2Co17, Nd2Fe14B, Sr6Fe2O3, TbFe2, Al-Ni-Co and their combinations can also be used as well as spinel ferrites of the Fe3O4, NiFe2O4, MnFe2O4, CoFe2O4 type or Yt-grenades GdIG (gadolinium-iron grenade) and combinations thereof.

Although such a wide range of magnetic materials can be used, soft magnets are preferred in certain embodiments of the invention.

The terminology "soft magnets" as used in this document refers to any material that exhibits ferromagnetic properties but has a residual induction that is substantially zero when exposed to a magnetic force. Soft magnets show a quick response to an applied magnetic field, but very low (coercive fields (He) = 4 - 23.873 A / m [0.05 - 300 ersted (Oe)]) or zero magnetic field characteristics or keep very low magnetic lines of force after the magnetic field has dissipated. In addition, as used in this document, the terminology "hard magnets (also called permanent magnets)" refers to any material that exhibits ferromagnetic properties and has long residual induction when exposed to a magnetizing force. A ferromagnetic material is any material that has a permeability significantly greater than 1 and that exhibits magnetic hysteresis.

The magnetic materials used to form the magnetic layers in the flakes and films of the invention preferably have a coercivity of less than about 159.155 A / m (2000 Oe), more preferably less than about 23.873 A / m (300 Oe). Coercivity refers to the ability of a material to demagnetize under the influence of an external magnetic field. The greater the coercivity value, the greater the magnetic field required to demagnetize the material after the field is removed. In certain embodiments of the invention, the magnetic layers used are preferably "soft" magnetic materials (readily demagnetized) as opposed to "hard" magnetic materials (readily demagnetized), which have higher coercivity. The coercivity of the films, pigments, or magnetic dyes of the color shifting structures of the present invention are preferably in the range from about 3.979 A / m to about 23.873 A / m (from about 50 Oe to about 300 Oe). These coercivities are lower than those for standard recording materials. Thus, the embodiments of the invention that use soft magnets in magnetic color shifting pigments and in magnetic color shifting pigments are an improvement on conventional technologies. The use of soft materials

The magnetic material in the pigment flakes allows for easier dispersion of the flakes without the formation of lumps.

The magnetic layer 22 has a suitable physical thickness from about 20 nm to about 3000 nm, and preferably from about 50 nm to about 150 nm.

Insulator layers 25 and 26 may consist of any suitable electrically insulating material such as a dielectric material or some semiconductor materials. For example, the insulator layers can consist of magnesium fluoride, alumina, nickel oxide, or combinations thereof, as well as any other insulating material that is suitable for use in a thin film making process and that has suitable electrical insulating properties.

The insulator layers are of effective thickness to significantly prevent corrosion of the pigment flake by breaking the electrical path between the metal reflector layer (which will be discussed later) and the magnetic layer of the pigment flake. Each layer of insulator has a physical thickness of at least about 10 nm, and preferably from about 20 nm to about 40 nm.

The reflector layers 27 and 28 may consist of different reflective materials. Presently preferred materials are one or more metals, one or more metal alloys or combinations thereof because of their high reflectivity and ease of use, although non-metallic reflective materials are also used. Examples (non-limiting) of suitable metallic materials for the reflector layers include aluminum, silver, copper, gold, platinum, tin, titanium, palladium, nickel, cobalt, rhodium, niobium, chromium, iridium, and combinations or alloys thereof. The reflector layers 24 and 26 have a suitable physical thickness from about 20 nm to about 1000 nm, and preferably from about 50 nm to about 100 nm.

The asymmetric thin film flake has a stacked thin film structure with the same layers on one side of the magnetic layer. In such an embodiment, the asymmetric flake comprises a magnetic layer 22, an insulator layer 25 covering the magnetic layer 22, and a reflector layer 27 covering the insulator layer 25. Each of these layers may be of the same materials and have the same thickness as described above for the corresponding petal layers 20. .

Opposing insulator layers may optionally be added to cover the reflector layers 27 and 28 of the petal 20. These opposing dielectric layers increase the durability, stiffness and corrosion resistance of the petal 20. Alternatively, a dielectric layer may be formed to form a closed structure. so as to substantially surround the reflector layers 27 and 28 and the magnetic layer 22. The dielectric layer (s) may be optionally transparent or may be selectively absorbing so as to contribute to the color effect of the pigment flake. Examples of suitable dielectric materials for such dielectric layers will be described later with reference to the embodiment of Fig. 2.

Fig. 2 shows a magnetic color shifting pigment flake 40 based on RMF according to a further embodiment of the invention. The flake 40 has a generally symmetrical multilayer thin film structure including coating layers on opposite sides of RMF 42 which has a five-layer structure as shown for RMF in Fig. 1. As shown in Fig. 2, the first dielectric layer 44 and the second layer. dielectric 46 are respectively placed on the opposite layers of RMF 42. The first absorber layer 48 and the second absorber layer 50 are respectively on each of the dielectric layers 44 and 46. RMF 42 can be made of the same materials as discussed above for RMF according to 1, and the dielectric and absorber layers of the petal 40 will be discussed in more detail later in this document.

The flakes corresponding to the flake 40 may be produced by a fabric covering process as described previously in which various layers of the flake 40 are sequentially deposited on the fabric material to form a thin film structure which is then cracked and removed from the fabric to produce a plurality of flakes.

The dielectric layers 44 and 46 act as separating portions in the thin-film stacking structure of the petal 40. The dielectric layers are fabricated to have an effective optical thickness to impart interference colors and the desired color change properties. The dielectric layers can optionally be transparent or they can be selectively absorbing contributing to the color effect of the pigment. Optical thickness is a well-known optical parameter defined as nd, where η is the refractive index of the layer and d is the thickness

Physical layer. Typically, the optical thickness of a layer is expressed as quarter wave optical thickness (QWOT) which is equal to 4 ηό / λ, where X is the wavelength at which the QWOT condition occurs. The optical thickness of the dielectric layers can vary from about 2 QWOT at a planned wavelength of about 400 nm to about 9 QWOT at a planned wavelength of about 700 nm, and preferably about 2-6 QWOT at 400-700 nm depending on the desired color change. The dielectric layers can have a physical thickness from about 100 nm to about 800 nm, and preferably from about 140 nm to about 650 nm, depending on the desired color characteristics.

Suitable materials for the dielectric layers 44 and 46 include materials having a "high" refractive index, defined herein as greater than about 1.65, as well as those having a "low" refractive index, defined herein as about 1.65 or less. Each of the dielectric layers can be formed from a single material or from various combinations of materials and arrangements. For example, dielectric layers may be made of only a low refractive index material or only a high refractive index material, a mixture or multiple sublayers of two or more low refractive index materials, a mixture or multiple sublayers of two or more high refractive index materials or a mixture or multiple sublayers of low and high refractive index materials. Moreover, the dielectric layers may be formed partly or wholly from stacks with high / low dielectric-optical properties, which are discussed in more detail below. When the dielectric layer is partially formed from a dielectric-optical stack, the remainder of the dielectric layer may be formed from a single material or from combinations and arrangements of different materials as described above.

Examples of suitable high refractive index materials for dielectric layers 44 and 46 include zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide (ZrO2), titanium dioxide (TiO2), diamond carbon, indium oxide (In2O3), oxide indium tin (ITO), tantalum pentoxide (Ta2O5), cerium oxide (CeO2), yttrium oxide (Y2O3), europium oxide (EU2O3), iron oxides such as iron (II) and (III) oxide (Fe3O4) and iron oxide (III) (Fe2O3), hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO2), lanthanum oxide (La2O3), magnesium oxide (MgO), neodymium oxide (Nd2O3), praseodymium oxide (Pr6On), oxide samarium (Sm2O3), antimony trioxide (Sb2O3), silicon monoxide (SiO), selenium trioxide (Se2O3), tin oxide (SnO2), tungsten trioxide (WO3), combinations thereof and the like.

Examples of suitable low refractive index materials for dielectric layers 44 and 46 include silicon dioxide (SiO2), aluminum oxide (AbO3), metal fluorides such as magnesium fluoride (MgF2), aluminum fluoride (AlF3), cerium fluoride (CeF3), lanthanum fluoride (LaF3), sodium aluminum fluorides (e.g .: Na3AlF6, Na5Al3F14), neodymium fluoride (NdF3), samarium fluoride (SmF3), barium fluoride (BaF2), calcium fluoride (CaF2), lithium fluoride (LiF), combinations thereof or any other a low refractive index material having a refractive index of about 1.65 or less. For example, monomers and organic polymers can be used as low refractive index materials, including dienes or alkenes such as acrylates (e.g., methacrylate), perfluoroalkenes, polytetrafluoroethylene (Teflon), fluoro ethylene propylene (FEP), combinations thereof, and the like.

It is known that several of the above-mentioned dielectric materials are usually present in non-stoichiometric forms, often dependent on the particular method used to deposit the dielectric material in the form of a coating layer, therefore the names of the above-mentioned compounds indicate the approximate stoichiometry. For example, silicon monoxide and silicon dioxide have nominal silicon: oxygen ratios of 1: 1 and 1: 2, respectively, but the actual silicon: oxygen ratio of a particular dielectric coating layer differs slightly from these nominal values. Such non-stoichiometric dielectric materials can be used in the magnetic pigment flakes of the invention.

As mentioned above, the dielectric layers can be formed from high / low dielectric-optical stacks that have alternating material layers with low reflectance (L) and high reflectance (H). When the dielectric layer is formed from a stack of high / low dielectric properties, the color change with respect to the angle will depend on the refractive indices of the combined materials in the stack. Examples of suitable systems stosowych for the dielectric layers include LH, HL, LHL, HLH, HLHL, LHLH, or in general (LHL) ¹ 'or ¹ (HLH) l wherein n = 1-100, as well as various multiples and combinations thereof. In these hundred10

For example, LH indicates distinct layers with a low refractive index and a high refractive index.

In an alternative embodiment, high / low dielectric stacks are fabricated with a refractive index gradient. For example, a stack may be formed from layers having a graded ratio low to high, graded ratio high to low, graded ratio [low to high to low, graded ratio [high to low to high, where n = 1-100 , as well as their combinations and multiples. The graded index is the result of a discrepancy in refractive index, such as high to low index or low to high index, of adjacent layers. The grading factor of the layers can be produced by changing the gases during the deposition or co-depositing of two materials (e.g. L and H) in different proportions. Various high / low optical stacks can be used to increase the color change efficiency, provide anti-reflection properties to the dielectric layer, and alter the possible color space of the pigments of the invention.

The dielectric layers 44 and 46 may be composed of the same material or of a different material, and may have the same or different optical or physical thickness for each layer. It is known that when the dielectric layers are composed of different materials or have different thicknesses, the flakes show different colors on each of their sides and the resulting mixture of flakes in pigment or ink mixture will show a new color which is a combination of two colors. The color obtained will result, according to the additive color theory, of the two colors coming from the two sides of the petals. In many petals, the resulting color will be an additive sum of two colors resulting from the random distribution of the petals having different sides in relation to the observer.

The absorber layers 48 and 50 of the petal 40 may be composed of any absorber material having the desired absorption properties, including materials that are uniformly absorbing or non-uniformly absorbing in the visible portion of the electromagnetic spectrum. Thus, selectively (non-uniformly absorbing) or non-selective (uniformly absorbing) absorbing materials may be used depending on the desired color characteristics. For example, the absorber layers may be formed of a metallic absorbent material non-selectively embedded in a thickness where the absorber layer is at least partially absorbing or translucent.

Examples (non-limiting) of suitable absorber materials include metallic absorbers such as chromium, aluminum, nickel, silver, copper, palladium, platinum, titanium, vanadium, cobalt, iron, tin, tungsten, molybdenum, rhodium, and niobium, as well as the corresponding oxides, sulfides and carbides. Other suitable absorber materials include carbon, graphite, silicon, germanium, cermet, ferric oxide or other metal oxides, metals mixed in a dielectric matrix, and other substances that are capable of acting as non-selective or selective absorbers in the visible spectrum. Various combinations, mixtures, compounds or alloys of the above absorber materials may be used to form the absorber layers of the petal 40.

Examples of suitable alloys of the above absorber materials include inconel (Ni-Cr-Fe), stainless steels, acid-resistant alloys from the Ni-Mo-Fe group (e.g. Ni-Mo-Fe, Ni-Mo-Fe-Cr, Ni-Si- Cu) and titanium based alloys such as titanium mixed with carbon (Ti / C), titanium mixed with tungsten (Ti / W), titanium mixed with niobium (Ti / Nb), titanium mixed with silicon (Ti / Si) and their combinations.

As mentioned above, the absorber layers may also consist of an absorbing metal oxide, metal sulfide, metal carbide, or combinations thereof. For example, silver sulfide is one of the preferred sulfide absorbing materials. Other examples of suitable compounds for the absorber layers include titanium-based compounds such as titanium nitride (TiN), titanium oxynitride (TiNxOy), titanium carbide (TiC), titanium nitride-carbide (TiNxCz), titanium oxynitride-carbide (TiNxOyCz), titanium silicide (TiSi2), titanium boride (TiB2), and combinations thereof. In the case of TiNxOy and TiNxOyCz it is preferably X = 0 to 1, y = 0 to 1 and z = 0 to 1, where x + y = 1 in TiNxOy and x + y + z = 1 in TiNxOyCz. For TiNxCz preferably x = 0 to 1 and z = 0 to 1, where x + z = 1. Alternatively, the absorber layers may be composed of a titanium based alloy disposed in a Ti matrix or may be composed of Ti disposed in a matrix of a Ti based alloy. titan.

It is known to any person skilled in the art that the absorber layers can also be made of a magnetic material such as a nickel-cobalt alloy or other magnetic materials previously described. This simplifies the production of the magnetic color shifting pigments by reducing the number of materials required.

PL 212 104 B1

Absorber layers are manufactured to have a physical thickness ranging from about 3 nm to about 50 nm, and preferably from about 5 nm to about 15 nm, depending on the optical constants of the absorber layer material and the peak shift desired. The absorber layers can be composed of the same material or different materials and can have the same or different physical thickness for each layer.

In an alternate embodiment of petal 40, an asymmetric color shifting flake may be depicted having a thin film stacked structure with the same layers on one side of RMF 42 as shown in Fig. 2. Accordingly, the asymmetric color shifting flake comprises RMF 42, a layer dielectric 44 lying on RMF 42 and absorber layer 48 lying on dielectric layer 44. Each of these layers may be composed of the same materials and may have the same thickness as described above for the corresponding petal layers 40. Furthermore, asymmetric color shifting flakes may be made by a fabric coating process as described above, wherein different layers are sequentially deposited on the fabric material to form a thin film structure which is then subjected to a fracture process and removed from the fabric to form a plurality of flakes.

In a further alternative embodiment, flake 40 may be formed without absorber layers. In this embodiment, the opposite dielectric layers 44 and 46 are formed from dielectric stacks with high / low (H / L) optical properties as described above. In this way, the dielectric layers 44 and 46 can be arranged such that the flake 40 has a shell structure: (HL / ZRMFĄLH) ⁰ , (LH / ZRMFĄHL) ⁰ , (LHL2 / RMFĄLHL)! (HLH ^ / RMFĄHLH ^ or other similar systems where n = 1-100 and the L and H layers are 1 wavelength (QW) at the desired wavelength.

As a general rule, galvanic corrosion occurs between two metals if the algebraic difference of their atomic potentials in the array of precious metals is greater than +/- 0.3 volts. The potential of the aluminum / nickel pair is -1.41 V, indicating that there is an aluminum galvanic corrosion driving force in a pigment having a seven-layer structure such as Cr / MgF2 / Al / Ni / Al / MgF2 / Cr when the pigment is either immersed in electrolyte solution or exposed to a humid environment. This 7-layer pigment is particularly sensitive to alkalis or other alkaline solutions. In order to reduce the corrosion of aluminum in such a pigment, electrical contact between dissimilar metals Al and Ni is eliminated by placing the insulating layers described in this document between dissimilar metals. In such a scheme, the seven layer pigment structure becomes a nine layer structure as shown in Fig. 2, in which two layers of insulator are interposed between the aluminum layer and the magnetic layer as shown below:

Cr / MgF2 / Al / MgF2 20 nm / magnetic composite / MgF2 20 nm / Al / MgF2 / Cr

In order to facilitate the production process, the two insulator layers in this variant may be made of magnesium fluoride, which is a component of the pigment dielectric layers. Manufacturing pigment with MgF2 insulator layers requires two additional steps of winding a polyester (fabric) reel with a partially covered multilayer stack and depositing layers of the magnesium fluoride insulator. In an alternative fabrication scheme, the aluminum and magnetic layers may be separated by depositing a 20 nm thick Al2O3 film by vaporizing reactive aluminum in the presence of oxygen.

In a further alternative fabrication scheme, the surface of the first reflector layer, such as aluminum, is oxidized and the surface of the magnetic layer above the oxidized reflector layer is oxidized thereby forming oxide films between dissimilar metals. For such a process, ion guns are installed a short distance after the aluminum source but in front of the source of the magnetic material. In this way, the first aluminum layer that has been deposited from the aluminum source on the first dielectric layer that has been deposited on the first absorber layer passes through the oxidizing zone where its surface is oxidized to form a dense aluminum oxide insulating film. Oxygen pressure, ion gun power, and polyester coil rewind speed are parameters used to control the thickness of the Al2O3 film. In the next step, a magnetic material (e.g. nickel) is deposited on top of an insulating Al2O3 film. In the oxidation zone, a dense layer of NiO is formed on the surface of the magnetic material, thus isolating the magnetic layer from the next second aluminum layer. The NiO layer is a p-type semiconductor, so it provides electrical separation of the nickel layer and the second aluminum layer. After depositing the second aluminum layer, a second layer 12 is formed

A dielectric layer such as a magnesium fluoride spacer followed by a second absorber layer such as a chromium absorber, forming an optical stack which has the following structure:

substrate / Cr / MgF2 / Al / Al2O3 / Ni / NiO / Al / MgF2 / Cr

The thickness of the insulating layers in the ion launcher approach may be less than about 20 nm because these layers have a higher density than thermally or reactive vapor deposited films. The advantage of this method is that it is very similar to the process used to make the seven-layer stack up to the point where the number of polyester turns passes through the coating machine, but the ion-firing process produces a robust nine-layer construction that resists corrosion in humid environmental conditions and in electrolyte solutions.

Fig. 3 shows a reflective magnetic encapsulated flake 60 (RME) according to a further embodiment of the invention. The RME flake 60 has a three-layer shell structure with a reflector layer 62 substantially surrounding and enclosing the structure of an insulator layer 63 that surrounds the magnetic core layer 64. An insulator layer 63 between the reflector layer 62 and the magnetic layer 64 prevents galvanic corrosion of the petal 60. In addition, with a magnetic layer disposed therein. inside the outer reflector layer, as shown in Figure 3, the optical properties of the reflector layer are not degraded and the reflector layer remains highly reflective.

RME 60 flake can be used as a pigment particle or it can be used as a core particle with additional layers applied over it. Reflector layer 62, insulator layer 63, and magnetic layer 64 may be composed of the same materials and may have the same thicknesses as previously described for the corresponding petal layers 20.

In an alternate embodiment of the petal 60, a dielectric layer may optionally be added to cover the reflector layer 62 to enhance the durability, stiffness, and corrosion resistance of the petal 60. The dielectric layer may optionally be transparent or may be selectively absorbent, thus contributing to the color of the petal. .

Fig. 4 shows alternative shell structures (with phantom lines) for a color shifting magnetic pigment flake 80, in the form of a closed structure based either on the RMF flake or the RME flake described with reference to Figures 1 and 3. The flake 80 has part of a magnetic core 82. which is either an RMF flake or an RME flake, which may be covered by a dielectric layer enclosing the structure 84 substantially surrounding a portion of the magnetic core 82. The absorber layer 86, which covers the dielectric layer 84, externally encapsulates the flake structure 80. Hemispherical dashed lines one by one side of petal 80 in Fig. 4 indicate that the dilelectric layer 84 and the absorber layer 86 may be formed as contiguous layers around the magnetic core portion 82.

Alternatively, the magnetic core portion 82 and the dielectric layer may be in the form of a flake core thin-film stack wherein the opposing dielectric layers 84a and 84b are preformed on the top and bottom surfaces but at least not on one side surface of the magnetic core portion 82. which is RMF with an absorber layer 86 enclosing a thin film stack in a structure. The encapsulation process may also be used to form additional flake layers 80 such as a cap layer (not shown). The pigment flake 80 shows a distinct color change such that the pigment flake has a first color at a first light or viewing angle and a second color different from the first color at a second light or viewing angle.

In a further alternative embodiment, flake 80 may be formed without an absorber layer. In this embodiment, the dielectric layer 84 is formed of contiguous high / low (H / L) dielectric-optical coatings similar to the dielectric-optical stacks previously described. Thus, dielectric layer 84 may have a shell structure (HL)! (LH)! (LHL)! (HLH) ⁿ or other similar systems where n = 1-100 and the L and H layers are 1 QW at the desired wavelength.

Various conventional coating processes may be used to form dielectric layers and absorber layers by encapsulating them into a structure. For example, suitable methods of forming the dielectric layer include vacuum evaporation, sol-gel hydrolysis, CVD in a fluidized bed, plasma jet technique on a vibrating pallet filled with particles, and electrochemical deposition. Suitable methods of forming the absorber layers include vacuum evaporation and sputtering onto a mechanically vibrating bed of particles, such as disclosed in US Patent 6,241,858 B1, which is incorporated herein by reference. Alternatively, the absorber coating may be deposited by pyrolysis decomposition of organometallic compounds or CVD-related processes that may be carried out in a fluidized bed. If no further comminution is performed, these methods result in a magnetic core encapsulated in a structure with dielectric layers and absorber layers around it. Various combinations of the above coating processes may be used in the manufacture of pigment flakes with multiple coatings closed in a structure.

Various modifications and combinations of the above variants are also within the scope of the invention. For example, additional dielectric coatings, absorber coatings, and / or other optical coatings may also be formed in any of the above variants to provide further desirable optical characteristics. Such additional coatings can provide the pigments with further color effects.

In addition, an optional transparent coating applied to the outer surface (s) in each of the above pigment variants may also be formed to increase durability. For example, Fig. 2 shows, in phantom lines, a first transparent overlay 52 on the absorber layer 50 and a second transparent overlay 54 on the absorber layer 48. Fig. 4 shows, in the phantom lines, an optional transparent overlay 90 surrounding the absorber layer 86. The transparent overlay may be applied to the absorber layer. consist of any suitable transparent material that provides protection, such as the high and low index dielectric materials discussed earlier as well as polymers such as acrylates and styrenes, glass materials such as silicate or borosilicate glasses, or combinations thereof. The transparent deposited coating can be formed to have a suitable physical thickness from about 5 nm to about 10 µm, and preferably from about 100 nm to about 1 µm.

Additional flake variants that may be modified to include an insulator layer between the magnetic layer and the reflector layer as described herein are disclosed in U.S. Patent Application No. 09/844261, filed April 27, 2001, "Multilayer Magnetic Pigments and Films" ".

The pigment flakes of the present invention can be dispersed in a pigment medium to form a dye composition that can be applied to a wide variety of articles or papers. Pigment flakes added to the medium produce a predetermined optical response by radiation incident on the surface of the solidified medium. Preferably, the pigment medium comprises a resin or resin mixture that can be dried or cured by thermal processes such as thermal cross-linking, thermal setting or thermal drying or photochemical cross-linking.

Suitable pigment media include various polymeric compositions or organic binders such as aikido resins, polyester resins, acrylic resins, polyurethane resins, vinyl resins, epoxy resins, styrenes and the like. Examples of suitable resins include melamine, acrylates such as methyl methacrylate, ABS resins (copolymers of acrylonitrile butadiene styrene), ink formulations and alkyd resin paints, and various mixtures thereof. The pigment medium also preferably comprises a resin solvent such as an organic solvent or water. The flakes combined with the pigment media produce a dye composition that can be used directly as paint, ink, or molding plastic. The dye composition can also be used as an additive to conventional paint, ink, or plastic materials.

In addition, the flakes may optionally be mixed with various additive materials such as conventional pigment flakes, particles or materials of different hue, color saturation and brightness to achieve the desired color characteristics. For example, the flakes may be mixed with other conventional pigments, either of the interference type or the non-interference type, to produce a range of other colors. This pre-mixed composition may then be dispersed in a polymeric medium such as paint, ink, plastic or other polymeric pigment carrier liquid for use in a conventional manner. Examples of suitable additive materials are disclosed in US Patent Application No. 09 / 844,261, which is also the subject of a previously referenced patent.

Color shifting magnetic flakes according to the present invention are particularly suitable for applications where dyes with high color saturation and durability are desired. Due to the use of magnetic flakes changing color in the dye composition, it can be

A highly saturated permanent ink or ink was prepared in which the variable color effects are perceivable to the human eye. The color shifting flakes of the present invention have a wide range of color shifting properties, including large variations in color saturation (degree of color purity) as well as large variations in hue (relative color) with varying viewing angles. In this way, an object colored with an ink containing color shifting flakes according to the invention will change color depending on a change in the viewing angle or the angle of the object relative to the viewing eye.

The pigment flakes according to the invention can be easily and economically used in paints and inks that can be applied to various objects or papers such as motor vehicles, currency and securities, home appliances, architectural structures, flooring, fabrics, sports materials, packaging / casing. electronics, product packaging, and so on. Color shifting flakes can also be used in the manufacture of colored plastic materials, coating compositions, stampings, electrostatic coatings, glass, and ceramics.

Generally, the films have a non-symmetrical thin film skin structure which may correspond to layer structures on one side of the RMF in any of the above described stacked thin film flakes. The films can be laminated to a variety of items or they can be formed on a carrier substrate. The films can also be used in the hot stamping technique where a thin film stack of foil is removed from the release layer of the substrate by using a heat activated adhesive and applying to the counter surfaces. The adhesive may either be applied to the surface of the film facing the substrate or it may be applied in the form of a UV activated adhesive to the surface to which the film will be adhered.

Fig. 5 shows the skin structure of the color change film 100 formed on the substrate 102 which may be any suitable material such as a flexible PET fabric, a carrier substrate or other plastic material. The film 100 comprises a magnetic layer 104 on the substrate 102, an insulator layer 106 on the magnetic layer 104, a reflector layer 108 on the insulator layer 106, a dielectric layer 110 on the reflector layer 108, and an absorber layer 112 on the dielectric layer 110. Magnetic, insulator, reflector, dielectric layer. and the absorber can be made of the same materials and can have the same thicknesses as described earlier for the corresponding layers in flakes 20 and 40.

The film 100 may be produced by coating a fabric with various layers sequentially deposited onto the fabric using conventional deposition techniques as described above to form a thin film structure of the film. A film 100 may be formed on the fabric release layer so that the film is then removed and attached to the surface of the article. The film 100 can also be manufactured on a carrier substrate, which may be a fabric without a release liner.

In addition, an optional transparent overlay may be formed on the films to increase durability. For example, Fig. 5 shows, in phantom lines, a transparent layer 114 applied to the absorber layer 112. The transparent overlay layer 114 may be comprised of any suitable transparent materials that impart protection, such as the materials previously described with of the invention and may have the same thickness range as these coatings.

Additionally, the films can be modified to include an insulator layer between the magnetic layer and the reflector layer as described in this document and are disclosed in Patent Application Serial No. 09/844261, at the same time being the subject of a patent pending previously cited. Other variations, such as various optical articles with paired optically variable structures, may also use magnetic pigment flakes and films. Such optical articles are disclosed in Application No. 09/844261. Various applications of magnetic pigments and films are also disclosed in Application Serial No. 09/844261.

To illustrate the present invention, the following examples are provided:

P r z k ł a d 1

Different samples of bright color shifting flakes with the same thickness of MgF2 and Cr but with different thicknesses of the insulator layer were produced by depositing thin film layers on the fabric. The thin-film layers were broken to form flakes that were reduced to a size of about 20 nm (average single flake size).

The first pigment flake sample had the conventional Cr / MgF2 / Al / MgF2 / Cr five-layer construction. The second sample of the pigment flake was magnetic and had a structure

With a seven-layer Cr / MgF2 / Al / Ni / Al / MgF2 / Cr. The third sample pigment flake was magnetic and had _two coating structure dziewięciowarstwową Cr / MgF 2 / Al / MgF 2 / Ni / MgF ² / Al / MgF 2 / Cr. The MgF2 insulator layers between the Al and Ni layers were 16 nm thick. The fourth pigment flake sample had the same nine-layer skin construction as the third sample, except that the MgF2 insulator layers between the Al and Ni layers were 23 nm thick. The fifth pigment flake sample had the same nine-layer skin construction as the third sample, except that the MgF2 insulator layers between the Al and Ni layers were 25 nm thick. The sixth pigment flake sample was magnetic and had a nine-layer Cr / MgF2 / Al / Al2O3 / Ni / Al2O3 / Al / MgF2 / Cr nine-layer coating structure. The Al2O3 insulator layers between the Al and Ni layers were 20 nm thick.

P r z k ł a d 2

The paint vehicle and primer pigments of the samples of Example 1 were mixed in a 9: 1 ratio to form the paint samples. The paint samples were spread over the polyester sheets with a blade. The dry 1 in 3 pieces of painted polyester were immersed in a 2% (w / w) aqueous NaOH solution for 10 minutes. The color of each sample was measured before and after the immersion test. The AE color difference was used to compare the samples tested. Color difference AE in the L * a * b * color space indicates the degree of color difference but not the direction and is determined by the equation: AE = [YL *) + (Δα *) + (Δ ^)] where ΔL *, Δα * , ΔΥ are the differences in the values of L *, a * and b *, respectively. The larger ΔE indicates the major color difference caused by the degradation of the thin film layers in the pigment flakes. In this example, ΔE is the color change caused by exposure to NaOH. Table 1 lists the color difference of all painted samples.

T α b e l α 1

A sample Pigment construction ΔΞ after NaOH 1 5-layer stack without dissimilar metals 34.20 2 7-layer stack without insulator layers 54.77 3 9-layer stack with 16 nm thick MgF2 insulator layers 59.93 4 9-layer stack with 23 nm thick _{MgF 2 insulator layers} 39.32 5 9-layer stack with 25 nm thick _{MgF 2 insulator layers} 31.34 6 9-layer stack with 20 nm thick Al2O3 insulator layers 34.00

As shown in Table 1, samples 2 and 3 had a significantly higher AE when immersed in NaOH than samples 4-6 which had thicker insulator layers. Samples 4-6 showed color differences that were comparable to sample 1, which did not contain dissimilar metals.

The present invention may be carried out in other specific embodiments without departing from its spirit and essential characteristics. The described variants are considered in all aspects merely illustrative and not limiting.

Claims (22)

1. A magnetic pigment flake comprising: a central magnetic layer having a first major surface, an opposite second major surface, and at least one side surface, a first reflector layer, and a second reflector layer, each including one or more metals or metal alloys, further comprising a first insulator layer disposed on the first the main surface of the magnetic layer and a first reflector layer disposed on the first insulator layer, a second insulator layer disposed on the second major surface of the magnetic layer and a second reflector layer disposed on the second insulator layer, wherein the first and second insulator layers comprise an electrically insulating material and have a thickness of at least 10 nm, the thickness of the magnetic layer is from 20 to 3000 nm and the thickness of the reflector layer is from 20 to 1000 nm; and the pigment flake exhibits a reflectance corresponding to the index It is reflected by the reflection of the first and second reflector layers, and exhibits magnetic properties that are dependent on the magnetic layer. 2. A magnetic pigment flake according to claim 1; The method of claim 1, wherein the first and second insulator layers touch and cover the side surfaces of the middle magnetic layer to surround the middle magnetic layer, and that the first and second reflector layers contact and surround the insulator layer that surrounds the middle magnetic layer. 3. A magnetic pigment flake according to claim 1; The method of claim 1, wherein the first and second insulator layers are provided only on the first major surface of the magnetic layer and the second major surface of the magnetic layer, or the first and second insulator layers are provided on the first major surface of the magnetic layer and the second major surface of the magnetic layer and on one the side surface of the magnetic layer. 4. A magnetic pigment flake according to claim 1; The method of claim 1, wherein the first and second reflector layers form part of an adjacent reflection layer surrounding the magnetic layer and the insulator layer. 5. A magnetic pigment flake according to claim 1; The method of claim 1 or 2, wherein the magnetic layer comprises a material with a coercivity of less than about 159.155 A / m (2000 Oe). 6. A magnetic pigment flake according to claim 1; The method of claim 1 or 2, wherein the magnetic layer comprises a material with a coercivity of less than about 23.873 A / m (300 Oe). 7. A magnetic pigment flake according to claim 1; The method of claim 1 or 2, characterized in that the magnetic layer comprises a material selected from the group consisting of iron, nickel, cobalt, gadolinium, terbium, dysprosium, erbium, and alloys or oxides thereof. 8. A magnetic pigment flake according to claim 1, The method of claim 1 or 2, wherein the magnetic layer comprises a material selected from the group consisting of Fe / Si, Fe / Ni, Fe / Co, Fe / Ni / Mo, and combinations thereof. 9. A magnetic pigment flake according to claim 1; The method of claim 1 or 2, wherein the magnetic layer comprises a material selected from the group consisting of SmCo5, NdCo5, Sm2Co5, Nd2Fe14B, TbFe2, and combinations thereof. 10. A magnetic pigment flake according to claim 1. The method of claim 1 or 2, wherein the magnetic layer comprises a material selected from the group consisting of Fe3O4, NiFe2O4, MnFe2O4, CoFe2O4, YIG, GdIG, and combinations thereof. 11. A magnetic pigment flake according to claim 1. The method of claim 1 or 2, wherein the insulator layers comprise a dielectric material. 12. A magnetic pigment flake according to claim 1, The process of claim 1 or 2, characterized in that the insulator layers comprise at least one material selected from the group consisting of alumina, magnesium fluoride, nickel oxide, and combinations thereof. 13. A magnetic pigment flake according to claim 1; The process of claim 1 or 2, characterized in that the reflector layers comprise a reflective material selected from the group consisting of aluminum, silver, copper, gold, platinum, tin, titanium, palladium, nickel, cobalt, rhodium, niobium, chromium, iridium, and combinations or alloys thereof. 14. A magnetic pigment flake comprising: a central magnetic layer having a first major surface, an opposite second major surface, and at least one side surface; a first reflector layer and a second reflector layer; each comprising one or more metals or metal alloys, further comprising a first insulator layer disposed on the first major surface of the magnetic layer and a first reflector layer disposed on the first insulator layer, a second insulator layer disposed on the second major surface of the magnetic layer, and a second a reflector layer disposed on the second insulator layer, wherein the first and second insulator layers comprise an electrically insulating material and have a thickness of at least 10 nm; the thickness of the magnetic layer is from 20 to 3000 nm and the thickness of the reflector layer is from 20 to 1000 nm; and comprises a first dielectric layer on the first reflector layer, a second dielectric layer on the second reflector layer, a first absorber layer on the first dielectric layer, a second absorber layer on the second dielectric layer; and the pigment flake shows a reflectance corresponding to the reflectance of the first and second reflector layers and exhibits magnetic properties depending on the magnetic layer, the pigment flake showing a distinct color change in that the pigment flake has a first color under A first light or viewing angle and a second color different from the first color on a second light or viewing angle. 15. A magnetic pigment flake according to claim 15; The method of claim 14, wherein the first and second dielectric layers comprise a dielectric material having a refractive index of 1.65 or less. 16. A magnetic pigment flake according to claim 1, The method of claim 14, wherein the first and second dielectric layers comprise a dielectric material having a refractive index greater than 1.65. 17. A magnetic pigment flake according to claim 1, The method of claim 14, wherein the first and second reflector layers form part of an contiguous reflection layer surrounding the magnetic layer and the insulator layers, the first and second dielectric layers form part of an contiguous dielectric layer surrounding the adjacent reflector layer, and the first and second absorber layers form part of the contiguous layer. surrounding the adjacent dielectric layer. 18. A magnetic pigment flake according to claim 18; The method of claim 14, further comprising a first transparent coating applied to the first absorber layer and a second transparent coating applied to the second absorber layer. 19. A magnetic pigment flake comprising: a central magnetic layer comprising a metal or metal alloy and a reflector layer comprising one or more metals or metal alloys and surrounding the central magnetic layer, characterized in that it comprises an insulator layer sandwiched between the central magnetic layer and a reflector layer surrounding the magnetic layer, wherein the layer the insulator comprises an electrically insulating material and is at least 10 nm thick; the thickness of the magnetic layer is from 20 to 3000 nm and the thickness of the reflector layer is from 20 to 1000 nm; and the pigment flake exhibits a reflectance corresponding to that of the reflector layer and exhibits magnetic properties depending on the magnetic layer. 20. A magnetic pigment flake according to claim 1, The process of claim 14, wherein the insulator layer comprises a dielectric material. 21. A magnetic pigment flake according to claim 1; The process of claim 14, wherein the insulator layer comprises a material selected from the group consisting of alumina, magnesium fluoride, nickel oxide, and combinations thereof. 22. A magnetic pigment flake according to claim 1; The method of claim 14, wherein the insulator layers are from about 20 nm to about 40 nm thick.